San Diego Natural History Museum--Your Nature ConnectionExhibits
ALL THAT GLITTERS: The Splendor and Science of Gems and Minerals

THE HISTORY

Gems and mineral finds in San Diego County

Pride of the West mine, 1900
Click to enlarge

When gold was discovered in the Sierra Nevada foothills in 1848, thousands swarmed west seeking their fortune. Hunger for gold turned California from a remote wilderness into a thriving hub. Twenty years after the ’49ers, San Diego County had its own gold rush after gold was spotted in a creek west of the town of Julian.

California is one of the few places in the world where crystallized gold is found in significant amounts. Most gold is locked up in surrounding rock, but in California, there was enough space in the rock for the gold crystals to grow, forming large crystals.

Where are gems and gold found in San Diego County?
Gold on quartz<br />
De Maria Mine, Placer California. <br />
10.6 cm tall, 8.2 cm wide.<br />
Photo by Tom Spann.
Click to enlarge

Much of the gems and gold in our region has been mined already. But the mines still lie nestled in the mountains to the east of San Diego. These mountains are made of volcanic rock that formed between 93 million and 120 million years ago. So the gems and gold mined there are around 100 million years old.

More about our geologic history

San Diego’s hidden treasure pockets
Our rugged mountains conceal natural marvels. Hidden gem pockets formed close to 100 million years ago in rock deposits called pegmatites. Pegmatites are rock formations caused by magma (molten rock) rising from deep in the Earth and penetrating existing rock near the surface. Under the right conditions, as the magma cools, gems can crystallize inside sealed pockets. Mining of California’s pegmatite deposits began in the 19th century. Miners tunnel into a pegmatite dike, find a pocket, and remove the gems by hand.

Gems that you might find in San Diego County

Tourmaline crystal with lepidolite, morganite, and albite.<br />
San Diego County, California. <br />
Photo by Van Pelt.
Click to enlarge

Tourmaline, our star local gem
A rosy stone put San Diego County’s mines on the map. Pink tourmaline was discovered in local pegmatite mines late in the 19th century. It was a lucky find. China’s Empress Dowager had a fondness for the gem, triggering a craze in her country. Before her death in 1911, 120 tons of tourmaline had been mined locally. Most of it was sent to China.The Himalaya Mine was California’s biggest producer of tourmaline at the dawn of the 20th century.

More about the Empress Dowager and pink tourmaline


Benitoite on Natrolite<br />
Gem Mine, San Benito County, California.<br />
2.4 x 2.1 cm. Stone: 3.53 Ct<br />
Photo by Tom Spann.
Click to enlarge
California’s state gem
The Golden State is home to a unique blue stone. It’s called benitoite, and it’s California’s official state gem. Benitoite was discovered in 1907 in San Benito County. Gem-quality specimens are found nowhere else.

Miners at first assumed the blue stones were sapphires. But mineralogists soon determined they were a new discovery. All the gem material has been mined from the Benitoite Mine. What little exists lies in the hands of collectors.

More about Southern California mining history